Syngas production through combined steam-dry reforming of raw bio-oil over a NiAl2O4 spinel derived catalyst

Abstract

The combined steam-dry reforming (CSDR) of raw bio-oil with NiAl2O4 spinel derived catalyst was studied to establish suitable conditions to combine the objectives of CO2 valorization and sustainable production of syngas with suitable H2/CO ratio for the synthesis of chemicals and fuels. The reactions were carried out in an equipment with two units, for controlled pyrolytic lignin deposition and reforming of the remaining oxygenates in an in-line fluidized bed reactor. The CSDR conditions were: 600–800 ºC; CO2/C molar ratio, 0–1.1; steam/carbon (S/C) molar ratio, 0.5–1.7; space time, 0.125 and 0.250 gcatalyst·h/goxygenates, and time on stream, 6 h. The CO2 conversion is positive in a wide range of operating conditions, and there is always a reduction of CO2 emissions compared to the SR process, even under conditions of CO2 formation. 800 ºC, CO2/C ratio of 1.1, S/C of 1.7 and space-time of 0.250 gcatalyst·h/goxygenates allow attaining near 80% oxygenate conversion, 7% CO2 conversion and 90% syngas yield with H2/CO ratio of 1.6. Lowering the S/C ratio to 0.5 noticeably increases the CO2 conversion (> 23%), but reduces the H2/CO ratio of the syngas produced (< 1). The amount, nature and location of coke were characterized with different techniques (XRD, TPO, N2 adsorption-desorption and SEM), being the amorphous coke derived from oxygenates cracking the main responsible of deactivation. Catalyst stability improves along with temperature and space time, slightly with the CO2/C ratio, but with low effect of S/C ratio.